The present invention relates to a method and a device for the investigation of textured surfaces. In this case the present invention is described with reference to the surfaces of vehicle bodies, but it is also stated that the device is also applicable to other surfaces such as for example the surface of floors or pieces of furniture. Textured surfaces are to be understood as being those surfaces which are not completely flat but rather have (regular or even statistically distributed) uneven portions or differences in height. The textured surface is thus characterized by a topography which as well as a lateral extension also [has] a vertical profile. The human eye, however, cannot evaluate such differences in height quantitatively in the micrometer range but only observes the effects of this texture.
Various devices and methods which detect unevenness of this type are known from the prior art. In this way, for example, so-called Hommel instruments are known which measure the uneven portions themselves. These devices are relatively complicated, however, and always require a mechanical contact with the surface to be investigated. In addition, other types of surface-measuring instruments are known, which, however, likewise measure the surface itself physically (in particular by sensing).
Furthermore, devices and methods of investigating surfaces are known from the prior art, which measure this surface optically in order to investigate parameters such as for example the colour, the brightness or the DOI (distinctiveness of image). Instruments of this type are used in particular in the range of quality assurance, in particular when differences are to be determined between two surfaces to be compared. In this case too, however, it is not so much the quantitatively existing difference which is decisive but rather the human perception.
The problem arises in this case that the results of these investigations are not always unambiguous. Furthermore, in the final analysis, instruments of this type are used to investigate surfaces in order to establish as objective as possible a picture of the surface as it also appears to an observer.
In this case the phenomenon occurs that during the optical detection of objects the brain of the human observer usually draws upon experiences which then allow the observer to evaluate surfaces in a precise manner. In this way, the human observer can estimate, by observation on the basis of his or her experience, the materials of which specific surfaces can consist.
The object of the present invention is therefore to make available a method and a device which permit an objective evaluation of a surface, in particular a textured surface, without a mechanical measurement of this surface having to be carried out.